1. Field of the Invention
The present invention relates to a high temperature thermal reactor utilized in thermal decomposition of precursor gases to liquid products and byproducts gases, and more particularly to the thermal decomposition of silane into silicon products and byproduct hydrogen gas.
2. Description of the Prior Art
There is currently a major effort to develop low cost solar arrays. A primary need is the rapid, high capacity production of good quality silicon at a competitive cost. Present state-of-the-art manufacturing processes for producing high purity silicon are generally carried out by high temperature reduction of trichlorosilane by hydrogen.
The trichlorosilane process requires two reactants and is designed for ingot production. For this prior process involving thermal decomposition of trichlorosilane, the silicon is collected by a deposition on heated electrodes, rods or other surfaces. Production rates are normally in the order of 10 grams per hour. The solid silicon produced by such a process is generally cast into solid shapes for later processing according to methods well-known to the prior art such as the Czochralski continuous liquid feed growth. This two-step process results in unnecessary handling and transportation of the solid silicon, where purity is a strict requirement.
There are many processes now in development for making high purity silicon more economically than the above process. Examples are the high-temperature reduction of silicon tetrachloride by sodium, or by zinc, or other reductant; and another example is the thermal decomposition of silane. All of these processes yield solid silicon. It is this formation of solid silicon that has caused many problems with clogging of apparatus and decreased thermal performances in the production of silicon.
It would be desirable to provide a thermal reactor which prevents or reduces almost entirely the problems encountered by solid silicon within the thermal reactor. It would be desirable to avoid the problems of transport and handling of solid silicon and the cost of re-melt. It would be desirable to provide a small thermal reactor unit which would produce a pure liquid silicon and which would be capable of portable operation. Such a portable thermal reactor could be placed, in required numbers, in the production area of ingot or ribbon growth for supplying pure liquid silicon routinely or at any time as required.
These goals of producing inexpensive, pure silicon by thermal decomposition can be obtained with a thermal reactor in which heat and the reactant silane are supplied in sufficient amount and in proper manner to provide the following overall reaction: EQU SiH.sub.4 .fwdarw.2H.sub.2 +Si(liquid),
to yield liquid silicon.